Re: Raid6 write performance

["H. Peter Anvin" <hpa@zytor.com>]

Michał Przyłuski wrote:
> 
> I'm afraid that might be incorrect.
> 
> Let's assume we want to write 100MB of data onto a 4 drive raid6.
> Let's divide 100MB of data into two parts, say A and B, each 50MB big.
> Writing the data on the raid, would mean writing:
> * A on disk1
> * B on disk2
> * XOR(A,B) on disk3
> * Q(A,B) on disk4
> That is actually assuming 50MB chunk, and whole chunk writes, etc.
> Each of written portions would have been 50MB in size. That sounds
> reasonable to me, as with 2 data disks, only half of data has to be
> written on each. The fact that disks are really striped with data, XOR
> and Q doesn't change the image in terms of amount written.
> 
> I do hope I had understood the situation correctly, but I'll be ever
> happy to be proved wrong.
> 

Ah, sorry, yes you're of course right.  I was thinking about latency,
not throughput, for some idiotic reason.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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